Unstable Stone in Mortal Shell 2: Location & Upgrade Guide

The Unstable Stone is a key upgrade material in Mortal Shell 2 that lets you permanently enhance your weapon’s damage and unlock new abilities. You find it by defeating elite enemies, looting hidden chests, and exploring optional areas, then spend it at the Forge in Fallgrim to upgrade your weapon. This guide covers every known location, how the upgrade system works, and how to prioritize your stones.

Formula

The Unstable Stone upgrade system follows a simple progression: each weapon has a base damage value (B), and each upgrade level adds a fixed percentage increase (P) to that base. The formula for damage at upgrade level n is:

Damage(n) = B × (1 + P × n)

Where:

• B = base damage of the weapon (shown in your inventory)
• P = upgrade percentage per level (varies by weapon, typically 5%–8%)
• n = current upgrade level (0 to 5)

For example, if a weapon has base damage 100 and P = 6%, then at level 3 the damage is 100 × (1 + 0.06 × 3) = 118. This formula is the same for all weapons; the only difference is the base value and the percentage per level.

Worked Example

Using the default values from the calculator above: finish time = 50 minutes, distance = 10 km. The average pace is calculated as time divided by distance:

Pace = 50 min ÷ 10 km = 5.0 min/km

Speed = distance ÷ (time in hours) = 10 km ÷ (50/60) = 12.0 km/h

So with those inputs, your average pace is 5:00 per kilometer and your average speed is 12 km/h. The calculator returns these two values, with pace shown as the headline result.

Where to Find Unstable Stones

Unstable Stones are rare, but you can find a fixed number per playthrough. The main sources are:

• Fallgrim Outskirts: Two stones – one in a chest near the Grisha arena, another on a corpse in the underground tunnel leading to the Crypt of Martyrs.
• Crypt of Martyrs: Three stones – one from the elite enemy before the boss, one in a secret room behind a breakable wall, and one from the boss itself (always drops).
• Seat of Infinity: Two stones – one in a chest in the upper library, one from the mini-boss in the flooded lower level.
• Eternal Narthex: One stone – in a chest guarded by two enemies near the exit.
• Side quests: Completing certain NPC quests (like the one from the Old Prisoner) rewards one stone.

In total, you can obtain 9 stones per playthrough, which is enough to fully upgrade one weapon to level 5 (requires 5 stones) and partially upgrade another.

How the Upgrade System Works

Upgrading a weapon in Mortal Shell 2 is done at the Forge in Fallgrim, using Unstable Stones and Glimpses (the game’s currency). Each upgrade level requires one stone and a certain number of Glimpses, which increases with each level:

• Level 1: 1 stone, 500 Glimpses
• Level 2: 1 stone, 1000 Glimpses
• Level 3: 1 stone, 2000 Glimpses
• Level 4: 1 stone, 4000 Glimpses
• Level 5: 1 stone, 8000 Glimpses

Each level increases damage by a fixed percentage (shown in the weapon’s stats). It also unlocks a new move or ability at certain levels (usually level 2 and 4). The upgrade is permanent and carries over to New Game+.

How to Choose Which Weapon to Upgrade

Since stones are limited, you should upgrade the weapon that best fits your playstyle. Consider these factors:

• Base damage: Weapons with higher base damage benefit more from percentage increases.
• Move set: If you rely on heavy attacks, choose a weapon with a strong heavy attack that gains a new combo at level 2.
• Speed vs. power: Fast weapons (like the Hammer and Chisel) scale well with upgrades because they hit more often, but slow weapons (like the Greatsword) get bigger per-hit increases.
• New abilities: Check the upgrade tree – some weapons unlock a useful parry or special attack at level 4.

In general, the Martyr’s Blade is a safe choice for first playthroughs because its high base damage and good scaling make it effective against most enemies.

Common Mistakes and Misconceptions

Many players waste stones or miss locations. Here are the most common pitfalls:

• Not exploring thoroughly: Several stones are hidden behind breakable walls or in optional areas. Use the map from the Old Prisoner to find them.
• Upgrading too early: You can’t reset upgrades, so don’t spend stones on a weapon you’ll replace later. Check the damage output before committing.
• Ignoring Glimpse costs: You need a lot of Glimpses for higher levels. Save up before you reach the Forge, or you’ll have to farm enemies.
• Believing stones are infinite: They are not. You get exactly 9 per playthrough, so plan ahead.

Also note that the Unstable Stone is different from the “Quenched� stone used for the special upgrade path – don’t confuse them.

Comparison with Other Upgrade Materials

Unstable Stones are the standard upgrade material, but there are two others:

• Quenched Stones: Used for a special upgrade path that adds elemental damage, but they are even rarer (only 3 per playthrough).
• Glimpses: Not a stone, but required for all upgrades. You get them from killing enemies and using Effigies.

The Unstable path is the only one that increases base damage and unlocks new moves. The Quenched path adds elemental effects but doesn’t change the move set. Most players prefer Unstable for raw damage.

Safety and Efficiency Tips

To make the most of your stones:

• Farm Glimpses before upgrading: The best farming spot is the area before the Seat of Infinity boss – enemies respawn and give decent Glimpses.
• Upgrade after major bosses: You’ll face tougher enemies after each area, so upgrade before tackling the next boss.
• Don’t hoard stones: If you have 5 stones, fully upgrade your main weapon – the damage boost is huge.
• Use the calculator above to compare damage at different levels for your chosen weapon, so you know what to expect.

Also, if you’re playing on New Game+, you can find additional stones in the same locations (they respawn), so you can eventually upgrade all weapons.

Frequently Asked Questions

How many Unstable Stones are in Mortal Shell 2?
There are 9 stones per playthrough, as detailed above. This is enough to fully upgrade one weapon and partially upgrade another.

Can I get more Unstable Stones after using them?
No, they are finite per playthrough. However, in New Game+ the same locations respawn, so you can collect them again.

What is the best weapon to upgrade?
The Martyr’s Blade is generally recommended for its high base damage and good scaling. However, if you prefer fast combat, the Hammer and Chisel works well too.

Do Unstable Stones carry over to New Game+?
Yes, any unused stones in your inventory carry over, and the upgrade levels on your weapons also persist.

Is there a way to reset weapon upgrades?
No, there is no reset option. Choose carefully before spending your stones.

What’s the difference between Unstable and Quenched stones?
Unstable Stones increase base damage and unlock new moves. Quenched Stones add elemental damage but don’t change the move set. Both are used at the Forge, but they are separate upgrade paths.

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in t | Finish time | min | 50 | 0
in d | Distance | km | 10 | 0
out pace | Average pace | min/km | t / d | 2
out speed | Average speed | km/h | d / (t / 60) | 2